Inches to Millimetres
Convert inches to millimetres instantly.
Inches to Millimetres (in to mm) Converter
1 inch = 25.4 millimetres
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- 1 in = 25.4 mm
- 5 in = 127 mm
- 10 in = 254 mm
- 25 in = 635 mm
- Centimetrescm
- Inchesin
- Centimetrescm
- Millimetresmm
- Inchesin
How it’s calculated
mm = in × 25.4
- Multiply the value in inches by 25.4.
- To go back, divide by 25.4 (or multiply by 0.03937007874).
- 1 in = 25.4 mm · 1 mm = 0.03937007874 in
Quick examples
1 inch = 25.4 millimetres · 1 mm = 0.03937 in
- 1 inch = 25.4 millimetres
- 5 inches = 127 millimetres
- 10 inches = 254 millimetres
- 25 inches = 635 millimetres
- 100 inches = 2,540 millimetres
Inches to millimetres conversion table
| Inches (in) | Millimetres (mm) |
|---|---|
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| 15 in | 381 mm |
| 20 in | 508 mm |
| 25 in | 635 mm |
| 30 in | 762 mm |
| 40 in | 1,016 mm |
| 50 in | 1,270 mm |
| 75 in | 1,905 mm |
| 100 in | 2,540 mm |
| 250 in | 6,350 mm |
| 500 in | 12,700 mm |
| 1,000 in | 25,400 mm |
About these units
Inch (in)
US & imperial (identical)
1 in = 0.0254 m (exact)
The international inch, defined as exactly 2.54 cm since 1959.
Source: NIST SP 811 / Handbook 44
Millimetre (mm)
SI (metric)
1 mm = 0.001 m (exact)
Defined as exactly 1/1,000 of a metre.
Source: BIPM SI Brochure (9th ed.)
Frequently asked questions
How do I convert inches to millimetres?
Use mm = in × 25.4. Multiply the value in inches by 25.4.
How many millimetres are in 1 inch?
1 inch (in) equals 25.4 millimetres (mm).
How many inches are in 1 millimetre?
1 millimetre (mm) equals 0.03937 inches (in); more precisely 0.03937007874.
What is 10 in in mm?
10 inches = 254 millimetres.
What is a inch?
The international inch, defined as exactly 2.54 cm since 1959.
What is a millimetre?
Defined as exactly 1/1,000 of a metre.
Related conversions
Formula: mm = in × 25.4. Factors last reviewed 2026-10-27.